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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id b128sm4353614wmb.25.2020.01.22.07.08.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jan 2020 07:08:56 -0800 (PST) From: Vitaly Kuznetsov To: Paolo Bonzini , Sean Christopherson Cc: kvm@vger.kernel.org, Jim Mattson , linux-kernel@vger.kernel.org, Liran Alon , Roman Kagan Subject: Re: [PATCH RFC 2/3] x86/kvm/hyper-v: move VMX controls sanitization out of nested_enable_evmcs() In-Reply-To: <9c126d75-225b-3b1b-d97a-bcec1f189e02@redhat.com> References: <20200115171014.56405-1-vkuznets@redhat.com> <20200115171014.56405-3-vkuznets@redhat.com> <6c4bdb57-08fb-2c2d-9234-b7efffeb72ed@redhat.com> <20200122054724.GD18513@linux.intel.com> <9c126d75-225b-3b1b-d97a-bcec1f189e02@redhat.com> Date: Wed, 22 Jan 2020 16:08:55 +0100 Message-ID: <87eevrsf3s.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > On 22/01/20 06:47, Sean Christopherson wrote: >>> Yes, it most likely is and it would be nice if Microsoft fixed it, but I >>> guess we're stuck with it for existing Windows versions. Well, for one >>> we found a bug in Hyper-V and not the converse. :) >>> >>> There is a problem with this approach, in that we're stuck with it >>> forever due to live migration. But I guess if in the future eVMCS v2 >>> adds an apic_address field we can limit the hack to eVMCS v1. Another >>> possibility is to use the quirks mechanism but it's overkill for now. >>> >>> Unless there are objections, I plan to apply these patches. >> Doesn't applying this patch contradict your earlier opinion? This patch >> would still hide the affected controls from the guest because the host >> controls enlightened_vmcs_enabled. > > It does. Unfortunately the key sentence is "we're stuck with it for > existing Windows versions". :( > >> Rather than update vmx->nested.msrs or filter vmx_get_msr(), what about >> manually adding eVMCS consistency checks on the disallowed bits and handle >> SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES as a one-off case by simply >> clearing it from the eVMCS? Or alternatively, squashing all the disallowed >> bits. > > Hmm, that is also a possibility. It's a very hacky one, but I guess > adding APIC virtualization to eVMCS would require bumping the version to > 2. Vitaly, what do you think? As I already replied to Sean I like the idea to filter out unsupported controls from eVMCS but unfortunately it doesn't work: Hyper-V actually expects APIC virtualization to work when it enables SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES (I have no idea how without apic_access_addr field but). I checked and at least Hyper-V 2016 doesn't boot (when >1 vCPU). -- Vitaly